Process planning method, process planning apparatus and recording medium

ABSTRACT

A process planning apparatus extracts a region to be machined based on the difference of the shape data before and after machining of the workpiece, replaces the extracted region into combinations of the predetermined machining features, allocates a predetermined fixed cycle to each of the replaced machining features, and applies an assessment function relating to a machining time and a life of the end mill to each of the combinations of the machining features to which the fixed cycles are respectively allocated, thereby selecting a group of the fixed cycles which makes an assessment value obtained by the assessment function optimum as the optimal process. By these steps, it becomes possible to design the process for causing the NC machine employing end mills as a cutting tool to perform a predetermined machining of a workpiece without relying on the experience of the designer, and without necessitating complicated work.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Nonprovisional application claims priority under 35 U.S.C. § 119(a)on Patent Application No. 2004-307397 filed in Japan on Oct. 21, 2004,the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process planning method which makesit possible to design an optimum process including the size of cuttingtools to be used and machining order in machining a workpieces into thedesired shape with a machine tool equipped with end mills serving ascutting tools. The invention also relates to a process planningapparatus constituted to perform the method mentioned above.Furthermore, the invention relates to a recording medium in whichcomputer programs are stored for executing the above-mentioned methodwith a computer.

2. Description of Related Art

An NC (Numerical Control) machine for moving a cutting tool along a toolpath defined in advance numerically relative to a workpiece fixed on amachine table and thereby machining the workpiece in a predeterminedmanner is extensively adopted for the cutting processes for machiningworkpieces into various configurations with end mills used as cuttingtools, besides drilling processes as for which the drills, are used ascutting tools, and tapping processes for which the taps are used ascutting tools.

When machining with the NC machine of the above-mentioned kind isimplemented, a process planning is performed first to determine cuttingtools to be used, machining processes with the respective cutting tools,and the contents of work in each machining process, according to a finalmachining shape. Next, an NC program is prepared to set tool pathsaccording to the results of the process planning, together with a feedrate in each part on the respective tool paths, and then machining isperformed by operating the cutting tools and machine table based on theservo control according to the NC program.

The applicant of the present invention has already proposed an NCprogram generating method applicable to the NC machine for which an endmills are used as a cutting tools (Japanese Patent Application Laid-OpenNo. 2003-263208 (2003)). This method includes the steps of: replacing afinal machining shape with a plurality of fixed cycles prepared in eachmachining process defined as the results of a process planning;estimating cutting force exerted on the end mill on a tool path assumedin the respective fixed cycles; and determining a tool path in which theestimated value converges into an proper value together with the feedrate in each portion of the tool path. According to the method, it ispossible to prepare the NC program in which both high machiningefficiency and high machining accuracy can be attained while reducingthe damage and excessive wear of the end mill, without relying on theoperator's experience, and without the complicated work being required.

On the other hand, there have been the following problems. A processplanning necessary in the pre-stage for preparing an NC program as abovehas so far been practiced by the designer versed in industrialtechnology based on his experience (past achievements), so the resultsof the actually prepared process planning depend on the faculty of thedesigner. Moreover, the results of the process planning prepared by theplanner having abundant experiences are not necessarily optimum.Therefore, there is no assurance that the NC program prepared by theafore-described method based on the results of such process planning andthe machining to be practiced according to such NC program are optimumfrom the ultimate viewpoint of reducing the composite machining costafter taking into account the machining time, the durability of the endmill, and the like. Thus, there has been the possibility of losing anopportunity of further reduction of the machining cost.

In recent years, attempts have been made to automate the processplanning by dividing the complicated machining shape into plural sortsof machining features of simple shape, but those attempts are no morethan to determine the order of eliminating the machining features basedon the past achievements. Accordingly, they are only used as auxiliarytools for planner having little experience.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made under such circumstances. An objectof the invention is to provide a process planning method which makes itpossible to design an optimum processes for causing an NC machine toperform predetermined machining of a workpieces with end mills used ascutting tools, without relying on the planner's experience, and withoutrequiring the complicated work. Another object of the invention is toprovide an apparatus to be used in the implementation of the method, andalso to provide a recording medium storing a computer program forimplementing the method.

An aspect of the invention is a process planning method for determininga process for performing predetermined machining of a workpiece using aplurality of types of end mills, the process including selection of theend mills to be used and an order of the machining, the methodcomprising the steps of: extracting a region to be machined based on adifference in shapes of the workpiece before and after the machining;replacing the extracted region with combinations of predeterminedmachining features; allocating a predetermined fixed cycle to each ofthe replaced machining features; and applying an assessment functionrelating to a machining time and a life of the end mills to eachcombination of the machining features to which the fixed cycle isallocated, thereby selecting, as an optimum process, a group of thefixed cycles which makes an assessment value obtained by the assessmentfunction optimum.

Another aspect of the invention is a process planning apparatus fordetermining a process for performing predetermined machining of aworkpiece using a plurality of types of end mills, process includingselection of the end mills to be used and an order of the machining, theapparatus comprising: a database in which a plurality of predeterminedmachining features and fixed cycles are stored; extracting means forextracting a region to be machined based on a difference of externallyprovided shape data of a workpiece before and after the machining;replacing means for replacing the region extracted by the extractingmeans with combinations of the machining features stored in thedatabase; allocating means for allocating the fixed cycles stored in thedata base, respectively, to the machining features replaced by thereplacing means; and means for applying an assessment function relatingto a machining time and lives of the end mills to each combination ofthe machining features to which the fixed cycle is allocated by theallocating means, thereby obtaining an assessment value by theassessment function.

Further another aspect of the invention is a process planning apparatusfor determining a process for performing predetermined machining of aworkpiece using a plurality of types of end mills, the process includingselection of the end mills to be used and an order of the machining, theapparatus comprising: a database in which a plurality of predeterminedkinds of machining features and fixed cycles are stored; and a computerto be connected to the data base, and capable of performing thefollowing operations of: extracting a region to be machined based on adifference of externally provided shape data of a workpiece before andafter the machining process; replacing the extracted region withcombinations of the machining features stored in the database;allocating the fixed cycles, respectively, to the replaced machiningfeatures; and applying an assessment function relating to a machiningtime and lives of the end mills to each combination of the machiningfeatures to which the fixed cycle is allocated, thereby obtaining anassessment value by the assessment function.

Still further another aspect of the invention is a computer memoryproduct readable by a computer to execute a method for determining aprocess for performing predetermined machining of a workpiece using aplurality of types of end mills, the process including selection of theend mills to be used and an order of the machining, the computer memoryproduct comprising: first step for extracting a region to be machinedbased on a difference in shapes before and after the machining of theworkpiece; second step for replacing the extracted region withcombinations of predetermined machining features; third step forallocating a predetermined fixed cycle to each of the replaced machiningfeatures; and fourth step for applying an assessment function relatingto a machining time and lives of the end mills to each combination ofthe machining features to which the fixed cycle is allocated, therebyselecting, as an optimum process, a group of the fixed cycles whichmakes an assessment value obtained by the assessment function optimum.

In the present invention as recited above, plural sorts of fixed cycleswhich can be practiced by end milling and the machining features thatcan be obtained by the combinations of these fixed cycles are set inadvance. At first, based on the differences in the shapes before andafter the machining of the workpiece, the machining region is extracted,the machining region is replaced with a combination of the machiningfeatures, and at least one fixed cycle is optionally allocated to therespective machining features. Next, the results of the allocations areapplied to the assessment functions associated with a machining time anddurable life of the end mill. Then, a combination of the machiningfeatures and an allocation of the fixed cycles in which an assessmentvalue indicating the overall machining cost obtained by the assessmentfunction is optimized are determined as the optimum process. Theassessment function may be the function for obtaining the pure machiningcost from the machine charge including labor cost, machining time, toolcost and consumption rate of tool. Alternatively, it may be a functionto determine a machining cost with taking an estimated profit intoaccount, after considering a selling price of the final product andmodifying the machining cost described above.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block view showing the configuration of the NC machineequipped with the process planning apparatus used in the implementationof the process planning method according to the present invention;

FIGS. 2A to 2F are illustrative views of the fixed cycle in the endmilling;

FIGS. 3A to 3D are illustrative views of the representative machiningfeatures;

FIGS. 4A and 4B are illustrative views of the examples of combinationsof the fixed cycles to the pocket machining feature;

FIG. 5 is a flow chart showing the practice procedure of the processplanning method according to the present invention;

FIG. 6 is an illustrative view of the selection procedure of themachining features;

FIGS. 7A to 7E are illustrative views of the selection procedure of themachining features;

FIGS. 8A to 8E are illustrative views of the selection procedure of themachining features;

FIGS. 9A to 9F are illustrative views of the selection procedure of themachining features;

FIGS. 10A to 10E are illustrative views of the selection procedure ofthe machining features;

FIGS. 11A to 11E are illustrative views of the selection procedure ofthe machining features;

FIG. 12 is a view to show the actual size of the final product used forthe evidencing experiment of the process planning method according tothe present invention;

FIGS. 13A to 13E are graphic charts showing the results of practice ofthe operation planning on each of the patterns 1 to 5 given in FIG. 7 toFIG. 11;

FIG. 14 is a graphic chart showing the results of the process plan basedon the optimum pattern;

FIG. 15 is a graphic chart showing the results of the process plan by aproduction engineer; and

FIG. 16 is a schematic view showing another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is explained in detail with reference to thedrawings illustrative of its embodiment hereinafter.

FIG. 1 is a block diagram showing the configuration of an NC machineequipped with a process planning apparatus to be used in theimplementation of the process planning method according to the presentinvention. As illustrated, a process planning apparatus 1 is composed ofa computer comprising: a CPU (Central Processing Unit) 10 as acalculation processor; a ROM (Read Only Memory) 11 in which theimplementation procedures of the process planning method according tothe present invention are stored; a RAM (Random Access Memory) 12 fortemporarily storing diverse variables necessary for the implementationof the process planning method according to the present invention; and adatabase 13 referred to in the implementation of the process planningmethod according to the present invention and an input & output (I/O)interface 14. This process planning apparatus 1 furter comprises aninput operation unit 15 such as keyboard, mouse, or the like to beoperated by an operator, and a display unit 16 such as a CRT display, aliquid crystal display, or the like for displaying various informationobtained in each step in the implementation of the process planningmethod according to the present invention.

The NC machine tool 2 comprises a bed 20 as a platform, a machine table21 supported on the bed 20 and freely movable in the two directions (Xdirection and Y direction) perpendicular to each other in a horizontalplane and a spindle head 23 supported by a column 22 standing on oneside of the bed 20 and freely movable in the vertical direction (Zdirection) in the position above the machine table 21. The end mill Eserving as a cutting tool is installed into a removable manner viaappropriate attaching means at the lower end of the spindle 24 droppingfrom the spindle head 23.

The machine table 21 is structured so as to move forward in eitherdirection of X and Y according to the rotation of the ball screw (notillustrated) driven for rotation by each of the table feed motors M1 andM2. The spindle head 23 is structured so as to move forward in thedirection Z according to the rotation of the ball screw (notillustrated) driven by the spindle head feed motor M3. Further, thespindle 24 is connected to a spindle motor M4 attached to the upperportion of the spindle head 23, so that the spindle 24 is driven forrotation around its axis together with the end mill E attached at itslower end according to the rotation of the spindle motor M4. In FIG. 1the spindle motor M4 is illustrated to be attached outside the spindlehead 23, however, in NC machines for high speed machining in recentyears, the spindle motor M4 is generally built inside the spindle head23.

The NC machine 2 having the above-mentioned configuration performsmachining as stated below. At first, the workpiece 5 as a machiningobject is fixed by position setting to a predetermined position on themachine table 21. With the end mill E being attached to the spindle 24of the spindle head 23, the end mill E is rotated by the spindle motorM4: the end mill E is moved relatively to the workpiece 5 fixed on themachine table 21 along a tool path predetermined numerically, by feedingin X and Y directions carried out by the rotation of the table feedmotors M1 and M2 and by feeding in Z direction carried out by therotation of the spindle head feed motor M3. By virtue of this, theworkpiece 5 is machined into a predetermined shape.

The NC program showing the tool path of the end mill E which isnecessary for this machining is prepared in the process planningapparatus 1, and is given to the servo controller 3 via an input andoutput interface 14. The servo controller 3 controls the table feedmotors M1, M2, the spindle head feed motor M3 and the spindle motor M4,thereby feeding the end mill E according to the NC program given fromthe process planning apparatus 1.

The process planning apparatus 1 shown in FIG. 1 is connected on linewith the CAD (Computer-Aided Design) system 4. In the CAD system 4,designing of the final products to be manufactured by machining theworkpiece 5 is performed, and the shape data of the final products andthe workpiece 5 to be output from the CAD system 4 as a result of thisdesigning is given to the process planning apparatus 1 through the inputand output interface 14.

In the process planning apparatus 1, using the shape data given from theCAD system 4, process planning for determining the machining proceduresfor the workpiece 5 is performed according to the process planningmethod of the present invention to be described later. The processplanning includes the steps of selecting the tool to be used,determining the work contents, and preparing the CL (Cutter Location)data in the respective procedure. Furthermore, in the process planningapparatus 1, the above-mentioned NC program is prepared based on theresults of the process planning as stated above and the machiningconditions input by an operation of the input operation unit 15.

In the configuration shown in FIG. 1, information is exchanged on lineamong the process planning apparatus 1, the servo controller 3 and theCAD system 4, however, these apparatuses may be configured off line toeach other, whereby information may be exchanged via an appropriaterecording medium such as a magnetic disk or an optical disk.Alternatively, the process planning apparatus 1 may be incorporated intothe CAD system 4, so that the processes from the shapes design of thefinal product, through the process plan, to the NC program preparationmay be carried out integrally.

In the process planning apparatus 1, the process planning methodaccording to the present invention is performed in the procedures givenbelow, whereby the process planning is carried out for determining themachining procedure of the workpiece. In the process planning method ofthe present invention, the operations of the end mill E in the machiningare limited to the combinations of plural kinds of preset fixed cycles.Here, the fixed cycles mean a machining cycle in which the tool pathpattern can be univocally determined according to the shapes before andafter the machining. When this fixed cycle is given, an NC program canbe prepared by setting the feed pitch and feed rate according to themachining conditions. FIGS. 2A to 2F are the illustrative views of thefixed cycles in the end milling process. As shown in these figures, whenan end mill E is used as a cutting tool, the fixed cycles include, forexample, the 6 kinds of fixed cycles.

A fixed cycle shown in FIG. 2A is a boring cycle using spiral path. Thisfixed cycle is used when a finished hole H having the desired diameteris formed by bringing the end mill E into direct contact with the innercircumference of a hole H0, and feeding the end mill E along thespirally curving shaped tool path PW which expands outwardly in anoptional feed pitch. More specifically, the aforementioned tool path PWis set so as to serially increase the radius in each path, however, itmay be set as an assembly of the circular tool paths whose radius isincreased stepwise in each path.

A fixed cycle shown in FIG. 2B is a grooving cycle using trochoid path.This fixed cycle is used when a longitudinal groove G having the widthcorresponding to a diameter of a prepared hole G0 by extending theprepared hole G0 having a circular section to one side in the radialdirection using the end mill E having the smaller diameter than that ofthe prepared hole G0. The end mill E moves forward along the tool pathPW set into trochoid curve shape which advances on one side by anoptional feed pitch and cuts the downstream side in the moving directioninto crescent shape in the respective paths.

A fixed cycle shown in FIG. 2C is a boring cycle using helical path.This fixed cycle is used when a finished hole H having deep bottom ofthe same diameter as a prepared hole H0 is formed, by bringing the endmill E into direct contact with the inner circumference of the preparedhole having a circular section, and feeding the end mill E along thespiral shaped tool path PW which advances at an optional pitch in thedirection of depth (Z direction), as shown by arrow mark in the drawing.

A fixed cycle shown in FIG. 2D is a corner cutting cycle. In this fixedcycle, when a corner part C of the machining region is machined into around shape having a desired diameter, the end mill E having a radius nolarger than that of the round shape is used, and the end mill E movesreciprocally along the corner part C as shown by an arrow mark in thedrawing, while exerting the feed at an optional pitch to the directionof approaching to the corner part C, as shown by white base arrow marksin the drawing.

A fixed cycle shown in FIG. 2E is a side milling cycle. This fixed cycleis for cutting the workpiece by an optional feed pitch by feeding theend mill E along the side surface S of the workpiece. This cycle is usedin combination with the aforementioned boring cycle using spiral pathand grooving cycle using trochoid path, when, for example, the innersurface of a recess provided in the workpiece is cut to expand therecess outwardly.

A fixed cycle shown in FIG. 2F is a whole width grooving cycle. Thisfixed cycle is a machining cycle for forming a groove having the width Wequal to the diameter D of the above end mill E, by feeding the end millE toward one side in the radial direction, and by cutting the workpiecein the whole width on the upstream side in the feed direction.

Though the side milling cycle and the whole width grooving cycle are notthe fixed cycles in a strict sense, they are to be treated in line withthe fixed cycle.

In the process planning method according to the present invention, whenthe machining shape of the workpiece 5 is given, the region to bemachined is divided into a plurality of machining features and acombination of the fixed cycles to be allotted to the respectivemachining features is determined.

FIGS. 3A to 3D are the illustrative views of the representativemachining features. FIG. 3A shows a shoulder machining feature forforming a down shoulder portion 5 a on one side of the top face of theworkpiece 5. FIG. 3B is a groove machining feature for forming apredetermined groove 5 b on the top face of the workpiece 5. FIG. 3C isa pocket machining feature for forming a pocket portion 5 c ofpredetermined depth on the top face of the workpiece 5. The groovemachining feature also includes a machining feature for forming a groove5 d in which only one side in the longitudinal direction is open, asshown in FIG. 3.

Generally, a plurality of combinations of the fixed cycles can beallotted to the machining features as shown above, and quite a largenumber of combinations of the fixed cycles are conceivable for machiningto obtain all the machining features existing on a workpiece 5. FIGS. 4Aand 4B are the illustrative views of an example of the combinations ofthe fixed cycles for the pocket machining feature.

In FIG. 4A, a prepared hole 51 having an optional diameter is formed onthe predetermined position inside the machining region 50 shown byalternate long and two short dashes line in the drawing. The preparedhole 51 can be formed during the boring cycle using helical path, and itmay be substituted by drilling when it is possible to use a drill as atool. Next, the thus formed prepared hole 51 is expanded to a largediameter hole 51 of circular section having a diameter corresponding tothe width of the machining region 50 during the boring cycle usingspiral path, followed by extending this large diameter hole 51 to oneside during the grooving cycle using trochoid path to form a long hole53 having a long diameter corresponding to the length of the machiningregion 50. Finally, the crescent shaped portions remaining on the fourcorners of the long hole 53 are removed by the corner cutting cycle tocomplete the machining over the whole regions of the machining region50.

In FIG. 4B, after forming the above-described prepared hole 51, theprepared hole 51 is extended on one side by a predetermined length toform a slot 54 having narrow width by the grooving cycle using trochoidpath in which an end mill of small diameter is used. Next, the slot 54is expanded by machining of the inner circumferential surface during theside milling cycle to form a long hole 55 ranging over the whole lengthand whole width of the machining region 50. Finally, the crescent shapedportions remaining on the four corners of the long hole 55 are removedduring the corner cutting cycle to complete the cutting over the wholeregions of the machining region 50.

FIG. 5 is a flow chart showing the implementation procedure of theprocess planning method according to the present invention by theprocess planning apparatus 1, more particularly, the implementationprocedure of the process planning method according to the presentinvention by the CPU 10 of the process planning apparatus 1.

The process planning apparatus 1 starts its motion according to thepredetermined operation of the input operation unit 15. At first, itaccepts the machining conditions given by the operation of the inputoperation unit 15 (Step 1), and accepts the shape data of the workpiece5 given from the CAD system 4 (Step 2).

The shape data given from the CAD system 4 are the shape data of theworkpiece 5 after completion of machining designed in the CAD system 4(hereinafter to be referred to as a final product), which may containthe shape data of the workpiece 5 before machining (hereinafter to bereferred to as a raw material). The machining conditions given from theinput operation unit 15 are the parameters to be necessitated for theprocess planning and preparation of NC program such as the materialquality of the raw material, size of the selectable end mill, material,and the like. The shape data of the above-described raw material may begiven by the operation of the input operation unit 15.

After completion of the accepting as described above, the processplanning apparatus 1 recognizes the difference of the shapes between theraw material and the final product and extracts the machining region(Step 3), and then selects the machining features including the order ofimplementation (step 4). This selection is applicable to the pluralkinds of machining features such as shown in FIGS. 3A to 3D. Theselectable machining features are registered in advance in the abovedatabase 13. The machining regions may be extracted as plural regions,and further, several kinds of selection are concerivable for theselection of the machining features carried out in a manner as shownbelow. Accordingly, the following procedures are repeatedly carried outon each extracted machining region, and at each selection of themachining features.

FIG. 6 to FIG. 11 are the illustrative views of the selection proceduresof the machining features. FIG. 6 shows a target final product 7. When arecess having the illustrated shape is formed on the top surface of theraw material 70 of rectangular block shape, as the final product 7, thewhole recess is extracted as a single machining region 71. For theillustrated machining region 71, five selection patterns of themachining features as shown below are conceivable.

In a first pattern shown in FIG. 7, at first, as shown in FIG. 7A, agroove machining feature for a groove passing across the center of theupper surface is selected. Next, as shown in FIG. 7B, a shouldermachining feature is selected to obtain the pockets of the same depth byexpanding the width of the central part of this groove to both sides,and then, as shown in FIG. 7C, a shoulder machining feature forexpanding the upper half part of the groove remaining on both sides ofthe pocket, and next, as shown in FIG. 7D, a one side opened groovemachining feature is selected for increasing the depth of theafore-described groove and extending to the inside of the pocket, andfinally, as shown in FIG. 7E, a one-side opened groove machining featureis selected for forming the groove of the shallower bottom than thepocket at the center of the two side surfaces of the pocket.

In a second pattern shown in FIG. 8, at first, as shown in FIG. 8A, apocket machining feature is selected so as to form a pocket of largearea at the center of the upper surface, and next, as shown in FIG. 8B,a groove machining feature is selected for forming the grooves of thesame depth at the center of the peripheral parts remaining on both sidesof the pocket, and subsequently, as shown in FIGS. 8C to 8E, a machiningfeature similar to that of the first pattern is selected.

In a third pattern shown in FIG. 9, at first, as shown in FIGS. 9A and9B, a pocket machining feature and a groove machining feature areselected in this order to form a pocket and a groove crossing at thecenter of the upper surface, and next, as shown in FIG. 9C, a shouldermachining feature is selected for obtaining the pockets having the samedepth by enlarging the crossing part of the pocket and the groove infour directions, and next, as shown in FIG. 9D, the pocket machiningfeature is selected again for increasing the depth of the enlargedpockets, and finally, as shown in FIGS. 9E and 9F, a groove machiningfeature is selected for increasing the depth of the open groovesremaining on both sides of the pocket having the increased depth.

In a fourth pattern shown in FIG. 10, at first, as shown in FIG. 10A, agroove machining feature is selected for forming a groove of wide widthand shallow bottom crossing the center of the upper surface, and next,as shown in FIG. 10B, a one-side open groove machining feature isselected for forming a groove of narrow width and deep bottom over thepredetermined length on both sides of the formed groove. Next, as shownin FIG. 10C, a shoulder machining feature is selected for forming thepockets of the same depth by enlarging the central part of the groovehaving shallow bottom to both sides. Next, as shown in FIG. 10D, apocket machining feature is selected for increasing the depth of theformed pocket, and finally, as shown in FIG. 10E, a one-side open groovemachining feature is selected for forming a groove having the shallowerbottom than the pocket at the center of both side surfaces of the pockethaving the increased depth.

In a fifth pattern shown in FIG. 11, at first, as shown in FIG. 11A, apocket machining feature is selected for forming a pocket having largearea at the center of the upper surface, and next, as shown in FIG. 11B,a one-side open groove machining feature is selected for forming agroove having the shallower bottom than the formed pocket at the centerof both side surfaces thereof, then, as shown in FIG. 11C, a groovemachining feature is selected for forming a shallow bottomed open grooveat the center of the periphery remaining on both end parts of thepocket, and next, as shown in FIG. 11D, a groove machining feature isselected for increasing the depth of the open groove, and finally, asshown in FIG. 11E, a one-side open groove machining feature is selectedfor further increasing the depth of the open groove so as to extend itto the inside of the pocket.

In step 3 of the flow chart shown in FIG. 5, a machining region 71 asshown in FIG. 6 is extracted. And, in step 4, selection of the machiningfeatures to the extracted machining region 71 is performed as shown inFIG. 7 to FIG. 11. Though the selection patterns of the machiningfeatures are countless, the number of the selected patterns can bedecreased by setting the optional restrictive conditions such as byexcluding the machining features which do not ultimately remain in thecorresponding part of the final product 7.

After completing the selection of the machining features in the manneras above, the selected machining features are arranged in order (step5). This arrangement is a processing in which, for example, when thefeature factors overlap, they are unified as a single block, and thosehaving the same configuration and size are arranged in a group in therespective block unit. For example, in the second pattern shown in FIG.8, the groove machining features on both sides of the pocket arearranged as an identical group.

Next, the process planning apparatus 1 performs operation designing onthe combination pattern of the selected machining features to calculatethe machining cost required for implementing the operation designing(step 6). Here, the operation planning is a processing forsegmentalization to allocate the fixed cycles shown in FIGS. 2A to 2F tothe respective machining features selected, as stated above. Themachining cost C_(m) is calculated by the steps of preparing the NCprograms for each one of a plurality of allocation patterns of the fixedcycles, selecting the end mill as a machine tool for each one of aplurality of the fixed cycles and obtaining the machining time and thedamage level of the end mill by deciding the tool path and feed rate, bymeans of an assessment function shown in the following equation, usingthe obtained machining time and the damage level of the end mill, andthe fixed costs including the machine charge, labor cost, and the toolcost, etc.C _(m) =c _(m) T _(m) +c _(L) L _(t) /L _(f)  (1)wherein,

c_(m): Machine charge and labor cost per hour (¥/h)

T_(m): Machining time (h)

c_(L): Cutting tool cost (¥)

L_(t): Life consumption rate of cutting tool

(When ΣL_(t)/L_(f)=1, it is considered to be the extinction of the toollife)

L_(f): Durable life of cutting tool

In the case where the selling price C_(k) of the final product isdecided, in addition to the calculation of the machining cost C_(m) bythe equation (1), profit rate P may be calculated by the followingequation:P=(C _(k) −C _(m))/T _(m)  (2)

On the other hand, in the case of the general final products whoseselling prices C_(k) fluctuate, instead of the profit rate to becalculated by the equation (2), a modified machining cost C_(s) may becalculated by taking the estimated profit defined by the equation (3)into account. The factor c_(p) in the equation (3) denotes a profit perhour (¥/h), which is for example obtainable in the process planningapparatus 1 as a fluctuation amount based on the selling price C_(k)given as an input on each machining time.C _(s) =C _(m) +c _(p) T _(m) =c _(m) T _(m) +c _(L) L _(t) /L _(f) +c_(p) T _(m)  (3)

For preparing the NC program to be used for calculation of the machiningcost above, the method disclosed in the foregoing patent document(Japanese Patent Application Laid-Open No. 2003-263208 (2003)) by theapplicant of the present invention may be used. According to the method,the anticipated values of the cutting force exerted to the end millwhich is moved by feeding according to the respective fixed cycles isobtained, and the tool path of the end mill is determined together withthe feed rate so as to maintain this anticipated value to be a propervalue. In this manner, it becomes possible to prepare an NC programwhich can attain both high machining efficiency and high machiningaccuracy while reducing the damage and excessive wear of the end mill,and the durable life of the end mill and the consumption rate to be usedfor calculating the machining cost by each equation given above can bepresumed in high accuracy.

After completion of calculation of the machining cost, the processplanning apparatus 1 examines whether or not other selection patterns ofmachining features are conceivable (step 7), and when another selectionpattern of other machining features is conceivable, the operationreturns to the step 5 to repeat the similar processing to the newselection pattern. On the other hand, when another selection pattern ofmachining features is not conceivable, examination is made as to whetheror not any other machining region exists or not (step 8), and whenanother machining region exists, the operation returns to the step 4 torepeat the similar processing to a new machining region.

When it is determined in step 8 that there does not exist any newmachining region, the operation advances to the step 9. In the step 9,for example, the selection pattern of the machining features in whichthe sum total of the machining cost C_(m) calculated by the aboveequation (1) as an assessment function becomes the minimum is adopted asthe result of the optimum process plan, and the NC program based on thisselection pattern is outputted to complete a series of process planningoperations.

In step 9, an optimization may be achieved by using the equation (2) forcalculating the profit rate P or the equation (3) for calculating themodified machining cost C3 as an assessment function. Here, in the casewhere the profit rate P is used, the selection pattern of the machiningfeature in which the profit rate P becomes the largest is adopted as aresult of the optimal process planning, and in the case where themodified machining cost C3 is used, the selection pattern of themachining feature in which the modified machining cost becomes thesmallest is adopted as a result of the optimal process plan. In the step9, calculation is performed for the assessment value (machining costC_(m), profit rate P or modified machining cost C3) using the assessmentfunction may be carried out to display the results in a lump in thedisplay unit 16, so that the selection of the ultimate machiningfeatures is made by the operator.

Next, explanation is given on the results of the process plan obtainedby implementing the process planning method according to the presentinvention, with the final product 7 shown in FIG. 6 taken as a subject.In FIG. 12 the actual dimensions of the final product 7 is shown. Theraw material 70 is a rectangular block made of the carbon steel S50C(J.I.S.) for structural use.

The machining conditions are as shown below.

-   Machine tool: Vertical machining center-   Cutting tool: (Al, Ti) N coated carbide solid end mill, φ10 to 20 (4    blades)-   Cutting Condition: Cutting speed of 175 m/min to 230 m/min (Cut-in    amount in the axial direction is no more than the diameter of the    end mill)

FIGS. 13A to 13E are the diagrams to show the results of obtaining themachining cost C_(m) by the equation (1) by executing the operationplanning to the respective patterns 1 to 5 shown in FIG. 7 to FIG. 11.In these diagrams the machining time and the cutting length are alsoshown. By comparison of these diagrams it can be seen that the machiningcost C_(m) becomes the minimum when the pattern 1 shown in FIG. 7 isselected. In this case, in the step 9 the pattern 1 is adopted as aresult of the optimal process plan.

FIG. 14 is a diagram showing the result of the process plan based on theoptimal pattern. Shown in this diagram is the results of the processplan which makes the modified machining cost C_(s) set by theabove-mentioned equation (3) minimum, along with the results of theprocess planning which makes the machining cost C_(m) set by theabove-mentioned equation (1) minimum. The modified machining cost C_(s)has been calculated on assumption of the profit c_(p) per hour to be0.3.

FIG. 15 is a graphic chart showing the result of the process plan by aproduction engineer. The results of the process planning shown in thisdiagram are those determined by the skilled engineer based on hisexperience in the past, on assumption that the final product 7 shown inFIG. 12 is processed under the entirely same machining conditions. Theresults of this process plan is utterly different from the results ofthe process plan shown in FIG. 14.

Table 1 shows the results of comparison of machining time and machiningcost in the case where the results of the process plans shown in FIGS.14 and 15 are adopted.

TABLE 1 Machining Machining Machine Tool time cost C_(m) Charge CostProfit (min) (¥) (¥) (¥) (¥) Process Plan 21 39,273  3,498 35,775 0 byEngineer Process 60.5 22,000 10,075 11,925 0 Plan without Estimation ofProfit Process Plan 53.0 (C_(s)) 8,833 14,744 2,650 with 26,227Estimation of Profit

As shown in this Table 1, in the results of the process plan accordingto the present invention using the equation (1) as an assessmentfunction (process plan without profit), the machining cost becomesminimum (¥22,000). This machining cost is close to ½ of the machiningcost obtained as a result of the process plan by the engineer (¥39,273).On the other hand, according to the machining time comparison, themachining time in the case of the process plan without estimation of theprofit is nearly three times of the machining time in the case of theprocess plan by the engineer. Comparison between FIG. 14 and FIG. 15shows that, in the process plan by the engineer, priority is given toreduction of the machining time, and rigorous feed rate and cut-inamount settings are applied to the end mill used as a cutting tool, sothat the increased cutting tool cost by these settings has induced anincrease in the machining cost C_(m).

Besides, as shown in Table 1, in the process plan using the equation (3)as an assessment function (process plan with estimation of profit), themachining cost and the machining time are respectively the intermediatevalues of other two results. These results are because of the fact that,under the environment in which an optional profit margin can beestimated per unit time, shortening of the machining time actsadvantageously.

In the above-mentioned embodiment, an apparatus (process planningapparatus 1) equipped with a hardware of exclusive use for theimplementation of the process planning method according to the presentinvention. However, the aforementioned procedures in the processplanning method according to the present invention may be recorded as acomputer program into a computer-readable recording medium. Thisrecording medium may be mounted on a general-purpose computer, wherebythe program may be loaded up. Then, the method according to theinvention may be implemented using the CPU and the RAM of the computeras the processing unit and the storage unit of the invention.

FIG. 16 is a schematic diagram illustrating such an embodiment. In thefigure, the numeral 8 denotes a recording medium such as an optical diskor a magnetic disk. In the recording medium 8, a computer program 80containing program codes for causing a computer to execute theprocedures corresponding to the respective steps shown in the flow chartof FIG. 5 is recorded.

The recording medium 8 is mounted on a disk 92 of a general purposecomputer 9 comprising inputting means 90 such as a keyboard and a mouse;and a displaying means 91 such as CRT display or a liquid crystaldisplay; whereby the program is read out by the computer. Accordingly,the computer program 80 stored in the recording medium 8 is loaded up tothe computer 9, whereby the computer 9 implements the process planningmethod according to the present invention.

In addition to the use of the recording medium 8, the loading-up of thecomputer program 80 to the computer 9 may be carried out in anotherappropriate method such as the use of another computer connected on linethrough a network such as the Internet.

As will be apparent from the detailed description given above, in theprocess planning method and process planning apparatus according to thepresent invention, the machining region extracted from the difference ofshapes before and after the machining of the workpiece is replaced withthe predetermined machining features; the fixed cycles are allocated tothe respective machining features so as to be recognized as an assemblyof the fixed cycles, whereby an assembly for making an assessmentfunction relating to the machining cost optimum is selected.Accordingly, an optimal process design for carrying out a predeterminedmachining on a workpiece can be obtained, which satisfies conditions ofminimizing the overall machining cost that takes into account themachine charge, tool cost, selling price of the final product, etc.without necessitating the designer's experience and complicated work.

Further, when the computer program stored in the recording medium of thepresent invention is loaded up to a general-purpose computer, theprocess planning method of the present invention is implemented. Thispermits the process plan satisfying conditions of minimizing the overallmachining cost to be implemented easily. These are the advantages of theinvention.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentinvention is illustrative and not restrictive, since the scope of theinvention is defined by the appended claims rather than by thedescription preceding them, and all changes that fall within metes andbounds of the claims, or equivalence of such metes and bounds thereofare therefore intended to be embraced by the claims.

The invention claimed is:
 1. A process planning method for determining aprocess for performing predetermined machining of a workpiece using aplurality of types of end mills, the method comprising the steps of:using a computing device to provide plural kinds of fixed cycles,defined as machining cycles, in which a tool path pattern can be fullydetermined by the computing device in an automated fashion according toshapes before and after the machining, and also to provide and fullydetermine plural kinds of machining features, defined as shapes, thatcan be obtained by one of, or plural combinations of the fixed cycles;extracting a region to be machined based on a difference calculated bythe computing device between shapes of externally provided shape data ofthe workpiece before and after the machining; replacing, in an automatedfashion, the extracted region with a plurality of combinations of theprovided and fully determined plural kinds of machining features;selecting a combination of machining features from among the pluralityof combinations of machining features from said replacing; arranging theselected machining features in order; allocating at least one fixedcycle to each of the selected machining features; and employing acomputing device to apply an assessment function relating to a machiningtime and a life of the end mills to each combination of the machiningfeatures to which a fixed cycle is allocated in order to generate anassessment value; and selecting, in an automated fashion, a group offixed cycles which improves efficiency of the machining process withrespect to at least one machining parameter, based on said assessmentvalue.
 2. The method of claim 1, wherein a group of fixed cycles isfurther selected in order to minimize a number of tools used.
 3. Themethod of claim 1, wherein a group of fixed cycles is further selectedin order to minimize machining time.
 4. The method of claim 1, wherein agroup of fixed cycles is further selected in order to minimize a timeany one tool is used.
 5. The method of claim 1, wherein said computingdevice is a digital computer equipped with CAD/CAM software.
 6. Themethod of claim 1, wherein the at least one machining parameter is ananticipated completion time of the workpiece.
 7. The method of claim 1,wherein said assessment value comprises a machine cost and a machinetime for at least one of said plurality of types of end mills.
 8. Aprocess planning apparatus for determining a process for performingpredetermined machining of a workpiece using a plurality of types of endmills, said apparatus comprising: a database in which a plurality ofpredetermined machining features and fixed cycles are stored; adetermination unit that provides, from said database, plural kinds offixed cycles, defined as machining cycles, in which a tool path patterncan be fully determined by a computing device in an automated fashionaccording to shapes before and after the machining, and that alsoprovides and fully determines, from said database, plural kinds ofmachining features, defined as shapes, that can be obtained by one of,or plural combinations of the fixed cycles; an extraction unit thatextracts a region to be machined based on a difference of externallyprovided shape data of the workpiece before and after the machining; aregion replacement device that replaces, in an automated fashion, theextracted region with a plurality of combinations of the provided andfully determined plural kinds of machining features stored in thedatabase; a feature selector that selects a combination of the machiningfeatures from among the combinations of features that the replacementdevice replaced said region with; a feature arranger that arranges theselected machining features in order; a cycle allocator that allocatesat least one of the fixed cycles stored in the database, respectively,to each of the selected machining features; and an automated assessmentunit that applies an assessment function relating to a machining timeand a life of the end mills to each combination of the machiningfeatures to which a fixed cycle is allocated, thereby obtaining anassessment value related to improving at least one machining parameter.9. The apparatus of claim 8, wherein said cycle allocator allocatesfixed cycles in order to minimize a number of tools used.
 10. Theapparatus of claim 8, wherein said cycle allocator allocates fixedcycles in order to minimize machining time.
 11. The apparatus of claim8, wherein said cycle allocator allocates fixed cycles in order tominimize a time any one tool is used.
 12. The apparatus of claim 8,wherein said computing device is a digital computer equipped withCAD/CAM software.
 13. The apparatus of claim 8, wherein the at least onemachining parameter is an anticipated completion time of the workpiece.14. The apparatus of claim 8, wherein said assessment value comprises amachine cost and machine time for at least one of said plurality oftypes of end mills.
 15. A computer memory product readable by acomputer, having a program of instructions executable by the computer todetermine a process for performing predetermined machining of aworkpiece using a plurality of types of end mills comprising: providingplural kinds of fixed cycles, defined as machining cycles, in which atool path pattern can be fully determined by the computer in anautomated fashion according to shapes before and after the machining,and also providing and fully determining plural kinds of machiningfeatures, defined as shapes, that can be obtained by one of, or pluralcombinations of the fixed cycles; extracting a region to be machinedbased on a difference in shapes of externally provided shape data of theworkpiece before and after the machining; replacing, in an automatedfashion, the extracted region with a plurality of combinations of theprovided and fully determined plural kinds of machining features;selecting a combination of machining features from among the pluralityof combinations of machining features from said replacing step;arranging the selected machining features in order; allocating at leastone fixed cycle to each of the selected machining features; and applyingan assessment function relating to a machining time and a life of theend mills to each combination of the machining features to which a fixedcycle is allocated, thereby selecting a group of fixed cycles whichresults in an assessment value related to improving at least onemachining parameter.
 16. The program of claim 15, wherein the at leastone machining parameter is an anticipated completion time of theworkpiece.
 17. The program of claim 15, wherein said assessment valuecomprises a machine cost and machine time for at least one of saidplurality of types of end mills.
 18. The program of claim 15, whereinsaid program is designed to work with a CAD or CAM program.